Below the limit of detection (<LOD)

Below the limit of detection (< LOD) means that the laboratory could not detect the chemical. This may have been because the chemical was not present at all or because it was present at such a low level that the laboratory could not measure it.

Chemical measured

Detection frequency (percent detected)

The percentage of study participants with a measurable level of a chemical in their blood or urine sample.

Geometric mean

The geometric mean is an estimated middle value of a set of numbers.This is different than the average, also called the "arithmetic mean". A geometric mean is sometimes calculated when the set of numbers contains some extreme values. For example, the geometric mean of the set of numbers "1, 2, 2, 3, 4, 5, 5, 6, 10, 100" is calculated by multiplying all ten numbers together and then raising to the 1/10th power, giving 4.8. To compare, the arithmetic mean is calculated by adding all ten numbers and dividing by 10, giving 14.

In the data tables, an asterisk (*) means the geometric mean was not calculated because the chemical was found in less than 65% of the study group.

Indicates exposure to

The chemical(s) listed in this column is the chemical(s) to which a person may have been exposed through various sources (e.g., via drinking water or use of a consumer product). This chemical is commonly called the parent chemical.

Limit of detection (LOD), wet-weight

The limit of detection (LOD) is the lowest level of a chemical that the laboratory can measure in whole blood, urine or serum. The wet-weight LOD is presented as an amount of a chemical per liter of a sample (for example, microgram of a chemical per liter of urine, or µg/L). This is often the way that biomonitoring results are reported as well (for example, µg/L urine or µg/L serum). In some cases, however, biomonitoring results are presented as lipid-adjusted concentrations (µg/g lipid) or creatinine-adjusted concentrations (µg/g creatinine). For these cases, the units for the wet-weight LOD will differ from the units used to report the biomonitoring results.

Number of people tested

The number of individuals whose blood or urine samples were analyzed for a particular chemical.

Sample collection date

Selected percentiles

A range of values calculated to show the distribution of measured chemical levels. See specific percentiles below for examples.

Selected percentiles - 25th

If the 25th percentile is 0.3 µg/L, for example, this means that 25% of participants had levels less than or equal to 0.3 µg/L.

Selected percentiles - 50th

If the 50th percentile is 0.6 µg/L, for example, this means that 50% of participants had levels less than or equal to 0.6 µg/L.

Selected percentiles - 75th

If the 75th percentile is 1.2 µg/L, for example, this means that 75% of participants had levels less than or equal to 1.2 µg/L.

Selected percentiles - 90th

If the 90th percentile is 1.5 µg/L, for example, this means that 90% of participants had levels less than or equal to 1.5 µg/L.

Selected percentiles - 95th

If the 95th percentile is 1.9 µg/L, for example, this means that 95% of participants had levels less than or equal to 1.9 µg/L.

Study group

A brief description of the people who provided blood and/or urine samples for analysis in a particular study.

Units

Human biomonitoring data are commonly reported as an amount of a chemical present in a specified volume of a bodily fluid (such as blood or urine). For example, a chemical measurement expressed in units of µg/L urine tells us the number of micrograms (µg) of the chemical present per one liter (L) of urine. Using standard units allows for comparison across different studies. For more examples, see definition for: Units used by Biomonitoring California.